malware ta making files with illegal characters?

--------------------------------------------------------------------------------

all of a sudden you can see on usb pen drive folder and filenames such
as >?<.%$$ and the size of files ranging to 2gb which is false because
flash is only 1gb, and the more you mess with it the more such files
appear(and you cannot copy,open,rename,delete or attach them )
However avg-free,NOD nor quickheal scan did not reveal anything(did
not scan boot sector though)
Any ideas please